Cellulose esters are used extensively in lacquer coatings, such as nail polishes, because they are compatible with many resins, solvents, and additives, they exhibit good gap-filling properties, they dry quickly, they exhibit low toxicity, and they form a very aesthetically-pleasing coating on a variety of substrates. Nail polishes include thermoplastic coatings which harden after application by the evaporation of the solvents contained in the polishes. The thermoplastic coatings have contained cellulose esters, resins, solvents, pigments and other additives. Because thermoplastic nail polishes are soft and easily scratched, they are often modified or "hardened" by addition of formaldehyde-based resins, as described in U.S. Pat. Nos. 5,424,061 (Pappas et al.), U.S. Pat. No. 4,749,564 (Faryniarz), and U.S. Pat. No. 4,712,571 (Renz et al.). Such resins can cause hardening of the nail coating to the point of film embrittlement and can even lead to release of formaldehyde, which can react with the nail surface. Many nail polishes use nitrocellulose as the major film former as described in U.S. Pat. Nos. 5,424,061 (Pappas et al.) and U.S. Pat. No. 4,749,564 (Faryniarz et al.). Nitrocellulose is well-known for its tendency to become embrittled and yellow over time, and even lead to staining or yellowing of the nails. Because of its flammability, nitrocellulose requires special storage and handling. Such disadvantages have served to prompt a search for suitable substitutes.
Because of their clarity, compatibility with many resins and solvents, gap filling properties, pigment wetting properties, and rapid solvent release, cellulose acetate, cellulose acetate butyrate, cellulose acetate propionate, and mixtures thereof may be substituted for nitrocellulose. Such is described in U.S. Pat. Nos. 3,483,289 (Michaelson et al.), U.S. Pat. No. 4,409,203 (Gordon et al.), U.S. Pat. No. 4,712,571 (Remz et al.), U.S. Pat. No. 5,130,125 (Martin), U.S. Pat. No. 5,424,061 (Pappas et al.), and U.S. Pat. No. 5,512,273 (Martin). However as with other thermoplastic films, those described in said patents are prone to scratching and have essentially no solvent resistance.
Photopolymerizable nail polish formulations are described in U.S. Pat. Nos. 3,896,014 (Rosenberg), U.S. Pat. No. 4,058,442 (Lee et al.), U.S. Pat. No. 4,682,612 (Giuliano), 4,704,303 (Cornell), and U.S. Pat. No. 5,407,666 (Patel). None describe the use of photopolymerizable cellulose esters or their use in nail coating applications. Some formulations described in said patents incorporate the use of non-polymerizable cellulose esters as a viscosity modifier, but these esters are unable to participate in a crosslinking process to form a hardened, scratch resistant coating.
For the foregoing reasons, there remains a need for nail coatings that are hardened by exposure to ultraviolet light, are scratch resistant, clear in clarity after application, and non-toxic after application.